-  ~* 


Issued  March  23,  1910. 


I'.  S.  DEPARTMENT  OF  AGRICULTURE 

BDREAD   OF   ENTOMOLOGY     CIRCULAR   No.  119. 

L.  O.  \  lOWARD.  Entomologist  and  Chirf  of  Bureau. 


T1IK   CLOVEE    ROOT-BORER 


K.  M.  WEBSTER, 

eal  and  Forage  Tnseci  Investigations. 


•ji'.i:    Cir   mt    m 


:.I\TIMG  OFFICE   :   1910 


B  UREA  U  OF  ENTOMOLOGY 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau . 
C.  L.  Marlatt,  Assistant  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 
R.  S.  Clifton,  Executive  Assistant. 
Chas.  J.  Gilliss,  ChieJ  <  lerk. 

F.  H.  Chittenden1,  in  charge  of  truck  crop  and  stored  product  inst  ct  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insi  ct  inx  stigations. 

\V.  D.  Hunter,  to  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 

A  .  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations . 

E.  F.  Phillips,  in  charge  of  bee  culture. 

I>.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 

Rolla  P.  Currie,  to  charge  of  editorial  ivorl. 

Mabel  Colcord,  librarian 

Cereal  and  Forage  Insect  Investigations 

F.  M.  Webster,  in  charg< 

Geo.   I.   Reeves,  YV.  J.   Phillips,  C.  N.  Ainslie,  E.  O.  G.  Kelly,  J.  A. 
IFvslop,  V.  L.  Wildermuth,  R.  A.  Vickery,  T.  II.  Parks,   Herbert 
Osborn,  agents  and  experts. 
[Cir.  110] 

(II). 


Circular  No.  1 19.    'Revision  of  Circular  No.  67.) 


United  States  Department  of  Agriculture, 

BUREAU    OF    ENTOMOLOGY, 

L.  O.   HOWARD,    Entomologist  and  Chief  of  Bureau. 


THE  CLOVEK   ROOT-BORER. 

Hylastinus  obscurus  Marsham. 

r. ,  F.  M.  Webstek, 
I    <'■::■  g,  of  C>  •  al  and  Fora  i    I  I       ligations. 

i  vri:<  )in  i  i  ion. 

The  clover  root-borer  {Hylastinus  obscurus  Marsham)  is  not  a 
native  of  America,  bul  has  been  introduced  from  Europe  and  lias 
established  itself  in  the  fields  of  red  clover  in  some  sections  of  the 
eastern  United  States,  as  well  as  throughout  the  Stales  of  Oregon 
and  Washington,  wherever  clover  is  grown.  Ii  frequently  commits 
serious  depredations  by  burrowing  in  the  roots,  thereby  destroy- 
ing the  plants.  It  has  long  been  known  in  Europe  as  a  clover  pest, 
Eichoff"  giving  its  distribution  as  Germany,  Aus- 
tria, France,  England,  and  the  Canary  Islands. 
Other  European  entomologists  have  also  written 
of  its  occurrence,  and,  according  to  Bach,  it 
infested   large   fields   of  clover  near  Odenbach>  i^^^Ss 

Germany,  in  1803,  an  occurrence  evidently  coin- 
cident with  its  description   In   Marsham  in  1S02. 

While  it  did  not  come  to  notice  in  America  as 
a  pest  until  about  1S7S,  when  it  was  found  in 
destructive  abundance  in  central  New  York,  it 
probably  occurred  in  this  country  long  prior  to 
that  date.  Dr.  A.  D.  Hopkins,  who  is  making  a  Fig.  i  The  clover  root- 
special  stn.lv  of  this  group  of  beetles,  riz,  the     ^f^T? 

r  s>         l  >  Adu  1  itural  size 

Scolytidae,  has  shown  the  writer  a  specimen,  from  ai  right.  (Author's  nius- 
thecoUection  of  the  late  Doctor  Fitch,  with  a  New     " 

York  label  attached  to  the  pin,  referring  to  a  note  which  he  has  1 □ 

unable  to  find.  In  all  probability,  however,  this  specimen  antedates 
the  discovery  of  the  insect  by  Riley  in  L878.  Besides,  owing  to  the 
obscure  habits  of  the  pest,  it  is  more  than  likely  t  hat  it  w  as  injurious 
to  clover  even  prior  to  this  date-  without,  however,  having  been 
detected  bj  farmers.  Even  at  present,  both  in  the  Middle  West 
ami  on  the  Pacific  coast,  where  it  is  mosl  destructive,  it  has 
attracted    httlc   attention,  die  effects  of  its  ravages   being  usually 


I  'i'    I  luropai  i  hen  Borkenkafer,  p.  '■>:,  L881. 

(1) 


attributed  to  adverse  meteorological  conditions.  The  pest  seems 
to  have  spread  much  more  rapidly  westward  than  southward,  as  it 
probably  occurs  in  the  East  nearly  to  the  Mississippi  River;  but  it 
has  attracted  no  attention  along  the  Atlantic  coast  south  of  Penn- 
sylvania. In  that  State,  however,  the  writer  found  it  abundant  around 
Chambersburg,  but  not  disastrously  so,  in  October,  1905.  It  has  not 
been  reported  at  all  from  the  vicinit}^  of  Washington,  D.  C.  It  is  cer- 
tainly not  seriously  injurious  in  the  New  Eng- 
land States  at  the  present  time,  the  late  Dr. 
James  Fletcher  reported  a  similar  state  of 
affairs  in  Ontario,  "Canada,  and  we  do  not 
receive  any  reports  of  its  occurrence  between 
the  Mississippi  River  and  the  Rocky  Mountains. 
In  Ohio,  West  Virginia,  Indiana,  and  south- 
ern Michigan  it  is  becoming  more  and  more 
destructive. 


Fig.  2.— The  clover  root-borer: 
Larva  or  grub.  Much  en- 
larged. (Author's  illustra- 
tion.) 


DESCRIPTION    OF   THE    INSECT. 


The  fully  developed  insect  is  a  small,  dark- 
brown,  hard-bodied  beetle,  shown  enlarged  in  figure  1. 

The  larva,  or  grub,  shown  enlarged  in  figure  2,  is  about  an  eighth 
of  an  inch  long,  dingy  white,  with  honey-yellow  head  and  brown  jaws. 

The  pupa  (fig.  3)  is  even  smaller  than  the  larva,  also  dingy  white, 
with  two  minute  spinous  projections  on  the  top  of  the  head  and  two 
somewhat  larger  ones  at  the  anal  extremity.  The  eggs  are  elliptical, 
white,  and  minute,  yet  large  enough  to  be  seen  with  the  unaided  eye. 


LIFE    HISTORY. 

In  the  East  there  is  certainly  but  one  generation  annually,  though 
this  appears  to  be  long  drawn  out,  and  scattering  indi- 
vidual larvse  and  pupa?  may  be  found  throughout  every 
month  of  the  year.  The  finding  of  eggs  as  late  as  Sep- 
tember 18  has  been  reported  from  Michigan.  As  a  rule, 
however,  the  insects  pass  the  winter  in  the  adult  stage 
(fig.  1)  within  the  roots  where  they  developed.  During 
May  they  abandon  the  old  roots  and  seek  out  fresh 
plants  or  fields  in  which  to  lay  their  eggs.  The  eggs 
are  mostly  deposited  between  the  middle  of  May  and 
June  20.  The  female  gouges  out  a  shallow  cavity, 
more  often  in  the  crown  of  the  plant,  sometimes  at 
the  sides  of  the  root  even  2  or  3  inches  below  the 
crow  n,  and  in  this  places,  singly,  hut  not  far  separated, 
about  half  a  dozen  pale  whitish,  elliptical,  very  minute 
eggs.  These  hatch  in  about  a  week,  and  the  larvae  (fig.  2)  for  a  time 
[Cir.  119] 


Fig.  3.— The  clover 
root  -  borer: 
Pupa.  Much  en- 
larged. (Au- 
thor's illustra- 
tion.) 


feed  in  the  excavation  made  by  the  mother,  hut  soon  burrow  down- 
ward into  the  root,  and  before  the  1st  of  August  the  majority  of 
them  have  become  fullj  grown  and  passed  into  the  pupal  stage 
(fig.  3).  B3  October  nearly  all  have  become  fully  developed  beetles, 
hut  they  make  qo  attempt  to  leave  the  plant  until  the  following 
spring.  Bach  states  thai  the  adults  fly  at 
Omegnen  in  March  and  April,  while  EichhofF 
has  observed  them  near  Mulhausen,  swarming 
during  the  warm  afternoons  aboul  the  middle 
of  June;  bul  these  observations  were  all  made 
in  differenl  parts  of  Europe.  In  our  own 
country,  in  Ohio,  the  adults  are  abroad  and 
have  been  swepl  from  clover  fields  early  in 
May:  bul  no  swarming  of  the  beetles  has  been 
observed,  though  it  is  clear  that  they  may 
migrate  about  that  time  of  the  vear. 


~r 


FOOD    PLANTS. 

In  Europe,  besides  red  clover  and  alfalfa, 
the  species  is  known  to  attack  Scotch  broom, 
Cytisus  Spartium  1  scoparius,  and  goat  root  or 
yellow-flowered  rest  harrow  (Ononis  natrix). 
In  America  it  has  so  far  been  especially  de- 
structive to  red  clover  (Trifolium  pratense), 
yet  with  the  recently  increasing  interest  in 
the  growing  of  alfalfa  (Medicago  sativa)  in 
the  Northern  States  it  may  be  expected  to 
become  destructive  to  that  crop  also.  Besides, 
it  is  known  to  attack  mammoth  clover  (Tri- 
folium medium)  and  alsike  (T.  Tiybridum). 
The  fact  that  it  also  injures  the  garden  pea 
will  be  very  suggestive  to  growers  of  peas  for 
canneries,  and  indicates  the  undesirability  of 
sowing  pea--  early  in  the  season  on  ground 
that  has  recently  keen  in  these  clovers  or 
lying  adjacent  to  the  infested  clover  fields.  Late-sown  peas,  how- 
ever, would  probablj  nol  become  sufficiently  large  to  invite  attack 
until  after  the  hectics  had  appeared  and  gone. 


Fig.  4.— 1  iwlng 

work    of    cl 
Slight 


METHOD    <  )F    ATTACKING    RED    I  LOV1  i: 

The  insect's  method  of  attack  is  well  illustrated  by  figure    I,  show- 
ing a  clover  root    spin   in    two,  exposing   the   excavations.      In   • 
of    extreme    abundance,    however,    almost    the    entire    main    root. 
except    the    hark,     is    eaten,    the    substance    being    displaced    by 

[Clr,  1  L9] 


excreta,  and  the  dead  top  either  becomes  detached  of  itself  or  is 
easily  broken  off  if  one  attempts  to  pull  up  the  plant.  It  will  be 
observed  at  once  that  until  the  roots  have  attained  sufficient 
dimensions  it  will  be  impossible  for  the  insect  to  attack  them.  Over 
the  territory  where  red  clover  is  grown  in  this  country  the  seed 
is  sown  either  during  late  winter  or  spring;  and  during  the  first  year 
the  roots  of  the  plants  have  not  yet  attained  sufficient  size  to 
accommodate  the  insects  at  the.  time  the  latter  are,  with  the  excep- 
tion, perhaps,  of  a  few  belated  individuals,  abroad  and  depositing 
their  eggs;  and  thus  the  plants  are  almost,  if  not,  indeed,  entirely, 
exempt  from  attack  the  first  year.  Hence  it  is  not  until  the  sum- 
mer of  the  second  year  that  the  plants  are  destroyed.  This  has  led 
European  entomologists  to  believe  that,  like  many  others  of  the  Scoly- 
tida?,  the  insect  does  not  attack  the  plant  until  the  latter  has  become 
weakened  by  age  or  is  diseased.  But  in  this  country,  at  least,  this 
can  not  be  true,  for  the  reasons  just  given.  It  is  not  improbable, 
however,  that,  as  between  two  plants  with  roots  of  the  requisite  size, 
an  unhealthy  one  would  be  preferred  by  the  beetles  rather  than  one 
in  a  thoroughly  vigorous  condition.  But  as  yet  there  have  been 
no  observations  tending  to  verify  this  hypothesis.  A  diseased  clover 
root,  or  one  that  has  begun  to  decline  from  effects  of  age,  is  first 
affected  at  the  heart ;  and,  as  will  be  observed  from  figure  4,  this  is  the 
part  first  attacked  by  the  root-borer. 

EFFECT  FPON  THE  PLANT. 

While  an  infested  clover  plant  sooner  or  later  succumbs  to  an  attack 
by  this  insect,  life  may  be  lengthened  or  shortened  by  meteorological 
conditions.  Thus,  if  the  spring  or  early  summer  is  very  dry,  the 
plants  begin  to  die  in  patches  late  in  June,  as  soon  as  the  hay  crop  is 
removed;  but  if  there  is  much  rain  during  this  period,  the  weakened 
plants  may  continue  to  live  until  winter,  dying  out  before  spring.  In 
either  case  the  farmer  is  likely  to  be  misled  and  to  attribute  the  loss 
to  the  weather.  The  summer  of  1005  was  not  a  dry  one.  Copious 
rams  fell  with  sufficient  frequency  to  enable  all  but  the  most  seriously 
affected  plants  to  survive.  A  prominent  seedsman  of  Indiana,  who 
was  much  among  clover  fields,  thus  described  the  situation  in  October: 

In  driving  around  this  year  and  examining  clover  fields,  we  have  found  that  several 
fields  which  apparently  should  have  pn  >dueed  an  immense  amount  of  seed,  or  al  least, 
say,  3  or  4  bushels  to  the  acre,     *  *    did  not  shake  out,  anythinm.     We  pulled  up 

some  plants  and  discovered  that  the  planl  broke  off  at  the  crown;  or  if  any  of  the  root 
did  come  with  it.  it  was  small  and  decayed.  ( 'n  close  investigation  we  discovered  a 
little  white  worm  which  seemed  to  be  in  abundance  and  working  amongst  the  roots. 
\\  e  not  iced  this  in  a  number  of  fields  and  have  been  wondering  what  it  was.  We  have 
;d-o  had  samples  of  clover  plants  from  other  seel  ions  of  I  ndiana  showing  these  condi- 
tions,  and  almost  invariably  the  yield  of  such  fields  was  less  than  a  bushel  per  acre, 
and  in  many  instances  hiillinu  was  abandoned  and  the  huller  taken  out  of  the  field. 
I  fir.  1  19] 


N  VI  I    a  \I      I.MMll  s. 

While  Doctor  Riley  found  the  larva  of  one  of  the  common  soldier 
beetles,  probably  Telephorus  MLineatus  Saj  ,  attacking  the  Ian  ae  of  the 
borer,  and  although  it  probably  has  other  enemies,  both  among 
insects  and  birds,  these  have  so  far  proven  of  little  economic  impor- 
tance. 

rui.\  ENTIVE    MKAsi  RES. 

The  only  preventive  measure  yel  tried  thai  gives  any  promise  of 
success  is  summer  fallowing  as  soon  as  the  hay  crop  is  removed. 

At  this  time  the  young  arc  in  an  immature  state  and.  if  deprived 
of  food,  musl  perish.  They  can  not  migrate  from  one  clover  root  to 
another,  and,  if  the  meadow  is  now  broken  up,  throwing  the  roots 
up  tn  the  hoi  sun  and  winds,  these  wither  and  dry,  thus  no  longer 
supplying  the  necessarj  sustenance,  at  this  time  so  imperative  to  the 
life  of  the  larvse,  and  they  perish.  Thus  an  invasion  of  a  new  field 
from  an  old  one  maj  be  prevented.  Bui  if  the  fallowing  be  delayed. 
even  for  a  few  weeks,  t  he  larva1  will  then  have  for  the  most  pari  passed 
into  the  pupal  stage,  during  which  no  food  is  required,  and  plowing  can 
have  little  or  no  ell'ect  upon  them.  This  measure,  together  with  the 
practice  of  allowing  clover  fields  to  stand  only  two  years,  would  soon 
reduce  the  pesl  to  subjugation  in  anj  community.  No  trouble  from 
its  work  seems  to  occur  in  pastures.  Once  brought  under  control, 
it   would  seem  thai   a  system  of  rotation  that   involves  mowing  for 

hay  and  seed  the   Qrsl   year,  and    pasturing  and   then   breaking  Up  the 

ground  the  following  year,  if  generally  followed  in  a  community, 
would  suffice  to  keep  the  pest  in  subjection.  Extermination  is  nol 
possible. 

Approved : 

James  Wilson, 

Secretary  <;/"  Agriadturt . 
Washington,  I).  ('..  January  l '.,  1910. 

[Cir.  119] 

o 


UNIVERSITY  OF   FLORIDA 


3  1262  09216  5561 


